Recently, as a wind turbine blade satisfying requirements for both lightweight and high strength, a wind turbine blade having a spar cap structure has been used, wherein a main structural member called the spar cap is disposed in a limited portion of the outer skin located around the area where the blade has a maximum thickness in cross section.
FIG. 6(A) is a cross sectional view of a wind turbine blade having such a spar cap structure. Referring to FIG. 6(A), a blade 100 includes an outer skin layer 1 which entirely covers a suction side and a pressure side of the blade, spar caps 2 and 2 arranged on the suction side and the pressure side, respectively, and lightweight core members 3 and 4 inserted into the outer skin layer 1 at four positions.
Shear webs 7, 7 for linking the spar cap 2 on the suction side and the spar cap 2 on the pressure side have their respective ends bonded to the inner sides of the spar caps 2 and 2.
To manufacture the blade 100 described above, as shown in FIG. 6(B), dry fiber fabrics 1s for forming the outer skin layer 1, sandwich core members 3a and 4a, and dry fiber fabrics 1a for forming the spar cap are laminated on one another on a mold 10, and are impregnated with resin under a vacuum process.
Then, on the inner sides of the spar caps 2 and 2 arranged on the suction side and the pressure side, the respective ends of the shear webs 7, 7 for linking the spar caps 2 and 2 are secured by bonding. The suction side and the pressure side of the blade are then bonded to each other at a leading edge 5 and a trailing edge 6 of the blade, and lastly, the outer periphery of the outer skin layer 1 is finished.
An example of a wind turbine blade having the above-described structure is disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2007-255366).
In manufacture of the wind turbine blade 100 as shown in FIGS. 6(A) and 6(B), however, the outer skin layer 1 and the spar cap 2 are laminated on the same mold in turn. The laminating processes cannot be performed in parallel.
The laminating processes are performed using a plurality of sheets of dry fiber fabrics each having a length of several tens of meters, taking a considerable amount of time.
Further, the long sheets for the outer skin layer 1 and the spar cap 2 are laminated on a curved inner surface of the mold, during which the non-adhesive sheets of dry fiber fabrics are laid over one another. As a result, misalignment and other defects would highly likely occur, leading to variation in precision of the products. Repairing such defects also requires a considerable amount of time.
Furthermore, in manufacture of the blade 100, the dry fiber fabrics 1s for the outer skin layer 1, the sandwich core members 3a and 4a, and the dry fiber fabrics 1a for the spar cap 2, which have been laminated on one another on the mold 10, are impregnated with resin under a vacuum process. Therefore, slacks generated in the fabrics during the laminating processes would likely cause manufacturing defects such as wrinkles in the fabrics upon completion of the resin impregnation.
Still further, in the case where the manufacturing defects, such as the wrinkles in the fabrics, are found at the inspection stage, repairing the defects will also require a considerable amount of time as well as a large number of man-hours.